Spectrally tunable detector

ABSTRACT

A spectrally tunable optical detector and methods of manufacture therefore are provided. In one illustrative embodiment, the tunable optical detector includes a tunable bandpass filter, a detector and readout electronics, each supported by a different substrate. The substrates are secured relative to one another to form the spectrally tunable optical detector.

FIELD OF THE INVENTION

[0001] The present invention relates to tunable detectors, and morespecifically, to spectrally tunable detectors and methods of manufacturetherefore.

BACKGROUND OF THE INVENTION

[0002] Optical filters are commonly used in a wide variety ofapplications. For example, optical filters are used to provide separateoptical “channels” in optical fiber networks. Optical filters are alsoused to monitor the spectral emission from the power plants and enginesto provide a level of combustion monitoring and control. Optical filterscan also be used in biological particle identification systems toprovide spectral resolution of the fluorescence needed for high levelsof discrimination of biological materials. These are just a few of themany applications for optical filters.

[0003] Many optical filters are formed from thin films that reflect ortransmit a narrow band of wavelengths. In many cases, such filters areconstructed from several hundred layers of stacked narrow band filters,which collectively reflect or transmit a narrow band of wavelengths.Arrayed waveguide gratings are also commonly used. A limitation of manyof these filters is that they are not wavelength tunable. That is, theoperative wavelength cannot be dynamically changed during operation toselect a different optical wavelength.

SUMMARY OF THE INVENTION

[0004] The present invention relates to spectrally tunable opticaldetectors and methods of manufacture therefore. In one illustrativeembodiment, the tunable optical detector includes a tunable bandpassfilter, a detector, and readout electronics, each supported by adifferent substrate. The substrates are secured relative to one anotherto form the spectrally tunable optical detector.

[0005] The tunable bandpass filter may include a top plate and a bottomplate. Both the top plate and the bottom plate may be adapted to includea reflective region, and may be separated by a separation gap to form aFabry-Perot cavity. When so provided, the tunable bandpass filter may beselectively tuned to a desired bandpass wavelength by moving the topplate and/or bottom plate relative to one another to change theseparation gap. This movement can be driven by an electrostatic force.The range of movement of the top and/or bottom plate can determine thespectral range of the selected wavelengths. In some embodiments, a lensis positioned adjacent the tunable bandpass filter to help direct and/orshape the incoming light beam.

[0006] In one illustrative embodiment, the top plate is suspended abovethe bottom plate by one or more supporting legs and/or posts. One ormore top electrodes are mechanically coupled to the top plate, and oneor more bottom electrodes are mechanically coupled to the bottom plate.The one or more bottom electrodes are preferably in registration withthe one or more top electrodes. When an electric potential is appliedbetween corresponding top and bottom electrodes, an electrostatic forceis generated to pull the top plate toward the bottom plate, whichchanges the separation gap of the Fabry-Perot cavity. In someembodiments, the movement to the top plate is provided by the temporarydeformation of one or more of the supporting legs that suspend the topplate above the bottom plate.

[0007] A detector is preferably disposed adjacent the tunable bandpassfilter. The detector receives the one or more wavelengths that arepassed through the tunable bandpass filter. Preferably, the detector issensitive to the entire spectral range of wavelengths that can beselected by the tunable bandpass filter, but this is not required.

[0008] In one embodiment, the tunable bandpass filter is supported by afirst substrate, and the detector is supported by a second substrate.The first and second substrates are preferably substantially transparentto the expected spectral range of wavelengths. On some embodiments, thefirst and second substrates are secured together in a back-to-backfashion. When arranged in this manner, the wavelengths of interest pass,in sequence, through the tunable bandpass filter, the first substrate,and the second substrate, before reaching the detector. Alternatively,and in other embodiments, the first and second substrates are securedtogether in a front-to-back fashion. When arranged in this manner, thewavelengths of interest pass, in sequence, through the first substrate,the bandpass filter, and the second substrate, before reaching thedetector. Other arrangements of the first and second substrates are alsocontemplated, including a back-to-front arrangement and a front-to-frontarrangement, as desired.

[0009] In some embodiments, readout electronics are provided on a thirdsubstrate. The readout electronics may be electrically connected to oneor more electrodes of the detector through, for example, one or morebump bonds, one or more wire bonds, a common carrier or package, etc.Alternatively, the readout electronics may be provided on the firstand/or second substrates, if desired.

BRIEF DESCRIPTION OF THE DRAWINGS

[0010]FIG. 1 is a schematic cross-sectional side view of an illustrativetunable bandpass detector in accordance with the present invention;

[0011]FIG. 2 is a schematic cross-sectional side view of anotherillustrative tunable bandpass detector in accordance with the presentinvention;

[0012]FIG. 3 is a schematic cross-sectional side view of anotherillustrative tunable bandpass filter in accordance with the presentinvention;

[0013]FIG. 4 is a layout of an illustrative bandpass filter inaccordance with the present invention;

[0014]FIG. 5 is a layout showing a support leg, posts and top and bottomelectrodes of another illustrative bandpass filter in accordance withthe present invention;

[0015]FIG. 6 is a layout showing a support leg, posts and top and bottomelectrodes of yet another illustrative bandpass filter in accordancewith the present invention;

[0016]FIG. 7 is a layout showing a support leg, posts and top and bottomelectrodes of another illustrative bandpass filter in accordance withthe present invention;

[0017]FIG. 8 is a schematic diagraph showing an illustrative controlcircuit for controlling a bandpass filter in accordance with the presentinvention;

[0018]FIG. 9 is a graph showing the calculated percent transmission ofthe tunable filter of FIG. 3 versus wavelength and gap;

[0019]FIG. 10 is a graph showing the calculated normalized response ofthe tunable bandpass detector of FIG. 3 versus wavelength;

[0020] FIGS. 11A-11F are schematic cross-sectional side views showing anillustrative method for making a tunable bandpass filter in accordancewith the present invention;

[0021] FIGS. 12A-12I are schematic cross-sectional side views showinganother illustrative method for making a tunable bandpass filter inaccordance with the present invention;

[0022] FIGS. 13A-13H are schematic cross-sectional side views showinganother illustrative method for making a tunable bandpass filter inaccordance with the present invention;

[0023] FIGS. 14A-14K are schematic cross-sectional side views showingyet another illustrative method for making a tunable bandpass filter inaccordance with the present invention;

[0024] FIGS. 15A-15C are perspective views of an illustrative assemblyof a tunable bandpass filter in accordance with the present invention;and

[0025]FIG. 16 is a perspective view of another illustrative assembly ofa tunable bandpass filter in accordance with the present invention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0026] The following description should be read with reference to thedrawings wherein like reference numerals indicate like elementsthroughout the several views. The detailed description and drawings arepresented to show embodiments that are illustrative of the claimedinvention.

[0027]FIG. 1 is a schematic cross-sectional side view of an illustrativetunable bandpass detector 10 in accordance with the present invention.The illustrative tunable bandpass detector 10 includes a tunablebandpass filter 12, a detector 14 and readout electronics 16, eachsupported by a different substrate. For example, the tunable bandpassfilter 12 is supported by a first substrate 18, the detector 14 issupported by a second substrate 20, and the readout electronics 16 aresupported by a third substrate 22.

[0028] In the illustrative embodiment, the tunable bandpass filter 12includes a Micro Electro Optical Mechanical System (MEOMS) etalon. TheMEOMS includes a top plate 24 and a bottom plate 26. The bottom plate 26may correspond to the first substrate 18, or other layers provided onthe first substrate 18, as desired. Both the top plate 24 and the bottomplate 26 may be adapted to include a reflective region. In FIG. 1, thetop plate includes a reflective region 28, which may include for examplea Distributed Bragg reflector that includes a semiconductor and/ordielectric mirror stack. Alternatively, the reflective region 28 maysimply include one or more metal layers, such as an Aluminum layer. Itshould be recognized that these are only illustrative, and that thereflective region 28 may be made from any suitable material or materialsystem that provides the desired reflectivity. Like the top plate, thebottom plate 26 may include a reflective region 30, which like above,may be made from any suitable material or material system that providesthe desired reflectivity.

[0029] The top plate 24 and the bottom plate 26 are preferably separatedby a separation gap 32 to form a Fabry-Perot cavity. To selectively tunethe tunable bandpass filter 12 to a desired bandpass wavelength, the topplate is preferably pulled toward the bottom plate 26, which changes theseparation gap 32. The range of movement of the top plate 24 relative tothe bottom plate 26 determines the spectral range of the wavelengthsthat can be selected. In some embodiments, a lens 34 is positionedadjacent the tunable bandpass filter 12 to help direct and/or shape theincoming light beam.

[0030] In a preferred embodiment, the top plate 24 is suspended abovethe bottom plate 26 by one or more supporting legs and/or posts 36. Inaddition, one or more top electrodes 38 may be mechanically coupled tothe top plate 24, and one or more bottom electrodes 40 may bemechanically coupled to the bottom plate 26. When an electric potentialis applied between corresponding top electrodes 38 and bottom electrodes40, an electrostatic force is generated to pull the top plate 24 towardthe bottom plate 26. This changes the separation gap 32 of theFabry-Perot cavity. In some embodiments, the electrostatic force causesone or more supporting legs 36 to deform, which provides the movement ofthe reflective region 28 of the top plate 24 relative to the bottomplate 26. In a preferred embodiment, the reflective region 28 isrelatively rigid to help prevent curvature across the reflective region28 when actuated.

[0031] The detector 14 is preferably disposed adjacent the tunablebandpass filter 12, and receives the one or more wavelengths that arepassed through the tunable bandpass filter 12. Preferably, the detector14 is sensitive to the entire spectral range of wavelengths that can bepassed through the tunable bandpass filter 12. In an illustrativeembodiment, the detector 14 is an AlGaN PIN photodiode, such asdescribed in co-pending commonly assigned U.S. patent application Ser.No. 09/275,632, to Wei Yang et al., filed Mar. 24, 1999, and entitled“BACK-ILLUMINATED HETEROJUNCTION PHOTODIODE”.

[0032] In the illustrative embodiment shown in FIG. 1, the tunablebandpass filter 12 is supported by the first substrate 18, and thedetector 14 is supported by a second substrate 20. The first and secondsubstrates are preferably substantially transparent to the expectedspectral range of wavelengths. The first substrate can be selected forits transmission properties allowing only the proper range ofwavelengths to be transmitted. In one illustrative embodiment, the firstsubstrate is Pyrex and the second substrate is sapphire. The first andsecond substrates may be secured together in a front-to-back fashion, asshown in FIG. 1. That is, the front side of the first substrate 18 isprovided adjacent to the back side of the second substrate 20. Bumpbonds 44 or the like may be used to secure the first substrate 18 to thesecond substrate 20, and to make any electrical connection therebetween,as desired. A dielectric seal 54 may be provided as shown to protect thetunable bandpass filter 12. In some embodiments, the dielectric seal 54provides a vacuum seal. Arranged in this manner, the wavelengths ofinterest pass, in sequence, through the first substrate 18, the bandpassfilter 12, and the second substrate 20, before reaching the detector 14.

[0033] Alternatively, and as shown in FIG. 2, the first and secondsubstrates may be secured together in a back-to-back fashion. That is,the back side of the first substrate 18 may be secured to the back sideof the second substrate 20. Arranged in this manner, the wavelengths ofinterest may pass, in sequence, through the tunable bandpass filter 12,the first substrate 18, and the second substrate 20, before reaching thedetector or detectors 14. Other arrangements of the first and secondsubstrates are also contemplated, including a back-to-front arrangementand a front-to-front arrangement, as desired.

[0034] In some embodiments, readout electronics are provided on a thirdsubstrate 22. The readout electronics are preferably fabricated usingconventional integrated circuit processing techniques. For example, thereadout electronics may be fabricated using a CMOS process on a siliconsubstrate 22. Metal pads may be provided to provide electricalconnections to the detector 14. In the embodiment shown in FIG. 1, bumpbonds 46 are used to electrically connect one or more electrodes(usually combinations of each pixel and a common ground terminal) of thedetector 14 to corresponding metal pads of the readout electronics. Thebump bonds may also be used to secure the third substrate 22 relative tothe second substrate 20, as shown. The third substrate may be mounted toa package 50, if desired. In the illustrative embodiment, bond wires 52are used to connect selected package pins to the readout electronics andthe electrodes of the tunable bandpass filter 12, as shown.

[0035]FIG. 2 is a schematic cross-sectional side view of anotherillustrative tunable bandpass detector in accordance with the presentinvention. The embodiment shown in FIG. 2 is similar to the embodimentshown in FIG. 1. However, unlike the embodiment of FIG. 1, the first andsecond substrates are secured together in a back-to-back fashion. Thatis, the back side of the first substrate 18 is secured to the back sideof the second substrate 20. Arranged in this manner, the wavelengths ofinterest pass, in sequence, through the tunable bandpass filter 12, thefirst substrate 18, and the second substrate 20, before reaching thedetector(s) 14. Another difference is that the detector 14 includes anarray of detectors. Such an array of detectors 14 may be used to capturean array of pixels to form an image, rather than a single pixel as shownin FIG. 1. While FIGS. 1 and 2 show some illustrative methods toassemble various components to form a tunable bandpass filter, it shouldbe recognized that any suitable method may be used, including thosefurther described below.

[0036]FIG. 3 is a schematic cross-sectional side view of an illustrativetunable bandpass filter in accordance with the present invention. Theillustrative tunable bandpass filter 60 includes a top plate 62 and abottom plate 64. Both the top plate 62 and the bottom plate 64 may beadapted to include a reflective region. In the illustrative embodiment,the top plate 62 includes a reflective region 66, which in theembodiment shown, includes a Distributed Bragg reflector that has asemiconductor and/or dielectric mirror stack. Likewise, the bottom plate64 may include a reflective region 30, which in the embodiment shown,extends across the entire surface of the bottom plate 64 and may includea Distributed Bragg reflector that has a semiconductor and/or dielectricmirror stack. Alternatively, the reflective regions 66 and 64 may simplyinclude one or more metal layers, such as an Aluminum layer. It shouldbe recognized that these are only illustrative, and that the reflectiveregions 66 and 64 may be made from any suitable material or materialsystem that provides the desired reflectivity.

[0037] As discussed above, the top plate 62 and the bottom plate 64 arepreferably separated by a separation gap 68 to form a Fabry-Perotcavity. To selectively tune the tunable bandpass filter 60 to a desiredbandpass wavelength, the top plate 62 is preferably pulled toward thebottom plate 64, which changes the separation gap 68. The range ofmovement of the top plate 62 relative to the bottom plate 64 determinesthe spectral range of the wavelengths of interest.

[0038] As shown in FIG. 3, the top plate 62 is suspended above thebottom plate 64 by one or more supporting legs and/or posts 70. Inaddition, one or more top electrodes 72 may be mechanically coupled tothe top plate 62, and one or more bottom electrodes 74 may bemechanically coupled to the bottom plate 64. The one or more topelectrodes 72 are preferably in registration with the one or more bottomelectrodes 74. A dielectric layer 76 may be provided over the one ormore bottom electrodes 74, and/or a dielectric layer 78 may be providedover the one or more top electrodes 72. These dielectric layers may helpprotect the top and bottom electrodes from environmental conditions, andmay help prevent a short when the top plate is fully actuated toward thebottom plate.

[0039] When an electric potential is applied between top electrodes 72and bottom electrodes 74, an electrostatic force is generated that pullsthe reflective region 66 of the top plate 62 toward the bottom plate 64to change the separation gap 68 of the Fabry-Perot cavity. In someembodiments, the electrostatic force causes at least part of thesupporting legs to at least temporarily deform to provide the necessarymovement of the reflective region 66.

[0040]FIG. 4 is a layout of an illustrative bandpass filter inaccordance with the present invention. The bottom substrate is notshown. The top plate includes a reflective region 100, which may includefor example a Distributed Bragg reflector with a semiconductor and/ordielectric mirror stack, one or more metal layers, or any other materialor material system that provides the desired reflectivity. In oneillustrative embodiment, the reflective region 100 includes aDistributed Bragg reflector that has a number of alternating layers ofZrO₂/SiO₂, HfO₂/SiO₂, or any other suitable material system. The bottomplate (not shown) also preferably has a reflective region that ispositioned below the reflective region 100 of the top plate to form aFabry-Perot cavity therebetween.

[0041] In the illustrative embodiment, the reflective region 100 of thetop plate is secured to a top support member 102. The illustrative topsupport member 102 has a ring that extends around and is secured to thereflective region 100. In the illustrative embodiment, the top supportmember 102 also includes four thin supporting legs 106. The thinsupporting legs 106 are used to suspend the ring and reflective region100 above the bottom plate. In the illustrative embodiment, the thinsupporting legs are mechanically secured to posts 104 a-104 d. Posts 104a-104 d preferably extend upward from the bottom plate and support thetop support member 102. The top support member may be, for example, SiO₂or any other suitable material or material system.

[0042] Each thin supporting leg 106 has an electrode region 108 thatsupports a top electrode, as shown. Each top electrode region 108preferably has an interconnect line that extends along the correspondingsupporting leg to a corresponding anchor or post 104. Each post 104a-104 d preferably provides a conductive path that electrical connectsthe interconnect lines of the top electrodes to correspondinginterconnect lines 110 on the bottom plate.

[0043] In the illustrative embodiment, the interconnect lines 110 on thebottom plate electrically connect each of the posts 104 a-104 d to acorresponding pad 112 a-112 d, respectively. Rather than connecting theposts to corresponding pads, it is recognized that the interconnectlines 110 may electrically connect the posts 104 a-104 d to one or moredriving circuits, if desired. In addition, it is contemplated that theinterconnect lines may be electrically tied together so that all of thetop electrodes are commonly driven.

[0044] Bottom electrodes are preferably positioned below each of the topelectrodes. In the example shown, interconnect lines 120 electricallyconnect each of the bottom electrodes to a single pad 114. Thus, in theillustrative embodiment, all of the bottom electrodes are commonlydriven. However, this is not required.

[0045] To tune the illustrative bandpass filter to a desired band ofwavelengths, an electrical potential is provided between the bottomelectrodes and the top electrodes. When an electric potential is appliedin such a manner, an electrostatic force is generated that pulls theelectrode region 108 of the top plate toward the bottom plate to changethe separation gap of the Fabry-Perot cavity. In some embodiments, theelectrostatic force causes the supporting legs 106 of the top supportplate 102 to deform to provide the necessary movement of the reflectiveregion 100. Preferably, the top support member 102 is relatively rigidto help prevent curvature across the reflective region 100 whenactuated.

[0046]FIG. 5 is a layout showing a support leg 116, posts 128 a-128 dand top and bottom electrodes of another illustrative bandpass filter inaccordance with the present invention. In this illustrative embodiment,support leg 116 is shown with one end attached to the top support member118 of a top reflective region, and the other end attached to a bridgeportion 124 of a top electrode 120. The illustrative top electrode 120is “H” shaped with a first electrode leg portion 122 a and a secondelectrode leg portion 122 b connected by a bridge portion 124. The firstelectrode leg portion 122 a is suspended above a bottom plate byelongated supporting legs 126 a and 126 b, which are connected to posts128 a and 128 b, respectively. The second electrode leg portion 122 b issuspended in a similar manner.

[0047] When a potential is applied between the first and secondelectrode leg portions 122 a and 122 b and a corresponding bottomelectrode 130, the elongated supporting legs 126 a-126 d deform at leasttemporarily down toward the bottom plate 130. Because the supporting leg116 is connected to the bridge portion 124, which is situated at acentral location with respect to the first and second electrode legportions 122 a and 122 b, the supporting leg 116 may not substantiallydeform when providing movement to the top support member 118. This mayhelp reduce any deformation of the top support member 118 when the topsupport member 118 is moving from an upward position toward the bottomplate.

[0048]FIG. 6 is a layout showing a support leg 136, posts and top andbottom electrodes of yet another illustrative bandpass filter inaccordance with the present invention. In this illustrative embodiment,the top electrode includes a first electrode portion 132 a and a secondelectrode portion 132 b, which are offset relative to one another asshown. Support leg 136 is shown with one end attached to the top supportmember 144 of a top reflective region, and the other end attached to abridge portion 134 of a top electrode 132. The bridge portion 134connects two adjacent ends of the first electrode portion 132 a and thesecond electrode portion 132 b, as shown.

[0049] When a potential is applied between the first and secondelectrode portions 132 a and 132 b and a corresponding bottom electrode138, the elongated supporting legs 140 a-140 d deform at leasttemporarily down toward the bottom plate. In this embodiment, anintermediate part of the first and second electrode portions 132 a and132 b preferably snap down, and in some embodiments, actually engage thebottom electrode 138. As more potential is then applied, the first andsecond electrode portions 132 a and 132 b may begin to roll down towardthe bottom electrode 138, which lowers the position of the supportingleg 136 and the support member 144. This rolling action may providegreater control over the movement of the top support member 144 relativeto the bottom plate.

[0050]FIG. 7 is a layout showing a support leg, posts and top and bottomelectrodes of another illustrative bandpass filter in accordance withthe present invention. FIG. 7 is similar to the embodiment shown in FIG.6, but has two separate bottom electrodes 148 and 150. During operation,a relatively high potential is applied between one of the bottomelectrodes, such as electrode 148, to cause an intermediate portion ofthe first and second electrode portions 152 a and 152 b to snap down,and in some embodiments, to actually engage the bottom electrode 148.With the first and second electrode portions 152 a and 152 b in thesnapped down position, the support member 154 is preferably in an uppermost position.

[0051] Then, smaller potential may be applied between the first andsecond electrode portions 152 a and 152 b and the other bottom electrode150. This potential may cause the first and second electrode portions152 a and 152 b to begin to roll down toward the bottom electrode 150,which like above, may cause the supporting leg 154 and support member156 to move to a lower position. As noted above, this rolling action mayprovide greater control over the movement of the top support member 156relative to the bottom plate.

[0052]FIG. 8 is a schematic diagraph showing an illustrative controlcircuit for controlling the bandpass filter of FIG. 4. A microcontroller160 provides four control words to a Quad Digital-to-Analog (D/A)converter 162. The Quad D/A converter 162 provides individual analogsignals to each of the capacitance sensors 164 a-164 d. In oneembodiment, the four capacitance sensors 164 a-164 b correspond to thefour pairs of top and bottom electrodes of FIG. 4. Alternatively,separate capacitance sensors may be provided. The individual analogsignals provide the necessary electric potential to pull the top platetoward the bottom plate by a desired amount to change the separation gapof the Fabry-Perot cavity. One advantage of providing individual signalsto each of the electrode pairs is to help control the tilt of the topplate. If tilt is not a concern, a single analog signal may be used tocommonly drive all four electrode pairs of FIG. 4.

[0053] Feedback signals may be provided from each of the capacitancesensors 164 a-164 b back to the microcontroller 160 through anAnalog-to-Digital (A/D) converter 168. The feedback signals may be usedto provide a measure of the capacitance between each electrode pair ofFIG. 4. The measure of capacitance is proportional to the separation gapbetween each electrode pair. When so provided, the microcontroller 160may adjust each of the four control words provided to the Quad D/Aconverter 162 so that the capacitance between each electrode pair issubstantially equal. This may help reduce and/or control the tilt in thetop plate relative to the bottom plate.

[0054]FIG. 9 is a graph showing the calculated percent transmission ofthe tunable filter of FIG. 3 alone versus incoming wavelength andseparation gap. The separation gap between the top plate and the bottomplate is shown across the top of the graph. The wavelength of theincoming light beam is shown across the bottom of the graph. Thepercentage of the incoming light that is transmitted through thebandpass filter is shown along the “y” axis. As can be seen, as theseparation gap increases, the peak wavelength that is transmittedthrough the bandpass filter also increases. Thus, the bandpass frequencyof the filter can be controlled by simply changing the separation gapbetween the top and bottom plates. It is recognized that otherseparations of a similar fractional wavelength can produce similareffects.

[0055]FIG. 10 is a graph showing the calculated normalized response ofthe tunable bandpass detector of FIG. 3 versus wavelength. Thewavelength of the incoming light is shown along the “X” axis, and thenormalized response is along the “Y” axis. A first curve 200 shows thenormalized response versus wavelength for a separation gap of 320 nm.Likewise, a second curve 202 shows the normalized response versuswavelength for a separation gap of 376 nm. The range of movement of thetop and/or bottom plate determines the spectral range of the wavelengthsof interest. In the example shown, the top and/or bottom plate can bemoved between a separation gap of 320 nm to 376 nm. This produces aspectral range of the bandpass filter from about 320 nm to about 355 nm.

[0056] Preferably, the response of the detector and transmission of thesubstrate is set to encompass the entire expected spectral range ofbandpass filter. Curve 204 shows such a spectral range. Curve 204encompasses the entire spectral range from about 320 nm to about 355 nmof the bandpass filter.

[0057] A number of illustrative methods are contemplated for forming atunable bandpass filter in accordance with the present invention. FIGS.11A-11F are schematic cross-sectional side views showing one suchillustrative method. Turning to FIG. 11A, a first substrate 200 and asecond substrate 202 are provided. The first substrate 200 is preferablya silicon wafer or some other suitable material. The second substrate202 is preferably a silica substrate, glass, Pyrex, sapphire or someother suitable material. The second substrate 202 is preferablyrelatively optically transparent to the desired wavelength of interest(such as UV).

[0058] Turning again to FIG. 11A, an etch stop layer 204 is provided onthe first substrate 200. The etch stop layer may be any type of etchstop layer, but in the illustrative embodiment, is preferablymolybdenum. Molybdenum is preferred because it can be easily removed,such as with hydrogen peroxide, to separate the first substrate from theremaining structure, as further described below. Next a support layer206 is provided. The support layer is preferably polysilicon, but anysuitable material will do. A buffer layer 208 may be provided if desireto help bond the mirror region to the polysilicon support layer 206, asfurther discussed below.

[0059] Next, a top mirror 210 is provided and patterned. The top mirroris preferably a Distributed Bragg reflector that includes asemiconductor and/or dielectric mirror stack. The Distributed Braggreflector may include, for example, a number of alternating layers ofZrO₂/SiO₂, HfO₂/SiO₂, etc. Alternatively, the top mirror may simplyinclude one or more metal layers, such as an Aluminum layer. It shouldbe recognized that these are only illustrative, and that the top mirrormay be made from any suitable material or material system that providesthe desired reflectivity.

[0060] Once patterned as shown, upper electrodes 212 are provided andpatterned. The upper electrodes 212 are preferably metal, such asaluminum, copper or some other suitable conductor. Conductive pads 214are then provided, as shown. Finally, a layer of polyimide 216 isprovided over the top mirror 210, upper electrodes 212 and conductivepads 214, as shown. (OK w/o deletion).

[0061] A bottom mirror 218 is provided and patterned on the secondsubstrate 202, as shown. The bottom mirror is preferably a DistributedBragg reflector that includes a semiconductor and/or dielectric mirrorstack. Alternatively the bottom mirror may not be patterned. Like thetop mirror 210, the Distributed Bragg reflector may include, forexample, a number of alternating layers of ZrO₂/SiO₂, HfO₂/SiO₂, etc.Alternatively, the top mirror may simply include one or more metallayers, such as one or more Aluminum layers. It should be recognizedthat these are only illustrative, and that the top mirror may be madefrom any suitable material or material system that provides the desiredreflectivity. In some embodiments, the bottom mirror 218 is notpatterned, and is left to cover the entire surface of the secondsubstrate 202.

[0062] Bottom electrodes 222 and bottom pads 220 are then provided andpatterned. Bottom electrodes 222 are preferably arranged to be inregistration with the upper electrodes 212. Likewise, bottom pads 220are preferably arranged to be in registration with the upper conductivepads 214. Bottom conductive pads 226 are preferably provided on top ofbottom pads 220, as shown. Bottom conductive pads 226 and top conductivepads 214 are preferably sized to provide the desired separation betweenthe top mirror 210 and the bottom mirror 218.

[0063] The bottom conductive pads 226 and top conductive pads 214 arepreferably formed using conventional metal film processing techniques.Since metal film processing techniques are typically accurate toAngstrom like thickness over short distances, the desired separation gapmay be achieved across the structure. Standoffs 230 may be provided tohelp prevent the top mirror 210 from engaging the bottom mirror 218during actuation of the bandpass filter, as further described below.

[0064] A first layer 232 of polyimide is then provided. The first layer232 of polyimide is heated and hard cured. A second layer of polyimide234 is also provided. Like the layer of polyimide 216 discussed above,the second layer of polyimide 234 is preferably only soft cured.

[0065] Next, the first substrate 200 is preferably brought intoengagement with the second substrate 202, as indicated by arrow 240. Theresult is shown in FIG. 11B. This step uses polyimide adhesion. Becausethe polyimide layers 216 and 234 are only soft cured, they remaindeformable. Preferably, the two substrates are assembled in a waferbonding process where heat, pressure and vacuum are applied. The vacuumhelps remove trapped constituents. The pressure is used to force the twosubstrates together. The heat (e.g. to 400 degrees C.) hard cures thepolyimide to form a fused substrate sandwich.

[0066] Next, and as shown in FIG. 11C, holes are etched through thefirst substrate 200, preferably down to the etch stop layer 204. Next,the etch stop layer 204 is removed to release the first substrate 200from the structure. When the etch stop layer 204 is molybdenum, ahydrogen peroxide solution can be used to remove the etch stop layer andrelease the first substrate.

[0067] Next, and as shown in FIG. 11D, holes 240 are etched through thepolysilicon layer, the buffer layer 208, the upper electrodes 212, andinto the upper conductive pads 214. Also, a window 244 is etched throughthe polysilicon layer and the buffer layer 208 to expose the top mirror210.

[0068] Next, and as shown in FIG. 11E, metal is deposited into theetched holes 240 to provide plugs 250 that make electrical contact toboth the upper electrodes 212 and the conductive pads 214. Besidesproviding an electrical connection, the plugs 250 also help pin thepolysilicon support layer 206 to the conductive pads 214. A final dryetch (e.g. an oxygen plasma etch) is used to removes the polyimidesacrificial layers 216, 234 and 232 to release the top structure fromthe bottom structure, as shown in FIG. 11F.

[0069] FIGS. 12A-12I are schematic cross-sectional side views showingyet another illustrative method for making a tunable bandpass filter inaccordance with the present invention. Turning first to FIG. 12A, abottom mirror 300 is grown on a substrate 302. The bottom mirror 300 ispreferably a Distributed Bragg reflector that includes a semiconductorand/or dielectric mirror stack. The Distributed Bragg reflector mayinclude, for example, a number of alternating layers of ZrO₂/SiO₂,HfO₂/SiO₂, etc. Alternatively, the bottom mirror may simply include oneor more metal layers, such as one or more Aluminum layers. It should berecognized that these are only illustrative, and that the bottom mirror300 may be made from any suitable material or material system thatprovides the desired reflectivity.

[0070] Next, and as shown in FIG. 12B, bottom electrodes 304 and bottomconducting pads 306 are provided. A dielectric or other protecting layer310 is then provided over the bottom electrodes 304 and bottomconducting pads 306. The dielectric or other protecting layer 310 isthen patterned to expose the bottom conducting pads 306, as shown.

[0071] Next, and as shown in FIG. 12C, a sacrificial layer 312 isprovided. The sacrificial layer 312 is preferably polyimide, but may beany suitable material. Next, and as shown in FIG. 12D, a top mirror 320is provided. The top mirror 320 is preferably a Distributed Braggreflector that includes a semiconductor and/or dielectric mirror stack.Like the bottom mirror 300, the Distributed Bragg reflector may include,for example, a number of alternating layers of ZrO₂/SiO₂, HfO₂/SiO₂,etc. Alternatively, the top mirror may simply include one or more metallayers, such as one or more Aluminum layers. It should be recognizedthat these are only illustrative, and that the top mirror may be madefrom any suitable material or material system that provides the desiredreflectivity. The top mirror 320 is then patterned, as shown in FIG.12E.

[0072] Next, and as shown in FIG. 12F, holes 324 are etched through thepolyimide layer 312 down to the conductive pads 306. Next, a metal layeris deposited and pattered to form top electrode regions 330. The metalextends into holes 324 to form an electrical connection with bottomconducting pads 306, as shown.

[0073] Next, and as shown in FIG. 12G, a support layer 340 is providedover the top surface of the structure. The support layer preferablybonds to the top mirror 320, and fills the holes 324. A buffer layer maybe provided first to help bond the layers, if desired. In a preferredembodiment, the support layer 340 is Si0 ₂.

[0074] Next, the support layer 340 is patterned to expose the top mirror320. Preferably the support layer 340 overlaps the outer perimeter ofthe top mirror 320, as shown. This overlap helps form a bond between thesupport layer 340 and the top mirror 320. Finally, and as shown in FIG.12I, a dry etch is used to remove the polyimide sacrificial layer 312 toreleases the top structure from the bottom structure, as shown. The dryetch is preferably an oxygen plasma etch. Note, the dielectric orprotective layer 310 may help prevent an electrical short between thetop electrodes 330 and the bottom electrodes 304 if they are drawntogether under electrostatic actuation. An anneal may be performed tohelp reduce the stress in the structure, including the SiO₂ supportlayer 340. The anneal can be performed before or after the polyimidesacrificial layer 312 is removed, as desired.

[0075] FIGS. 13A-13H are schematic cross-sectional side views showinganother illustrative method for making a tunable bandpass filter inaccordance with the present invention. Turning first to FIG. 13A, abottom mirror 400 is grown on a substrate 402. The bottom mirror 400 ispreferably a Distributed Bragg reflector that includes a semiconductorand/or dielectric mirror stack. The Distributed Bragg reflector mayinclude, for example, a number of alternating layers of ZrO₂/SiO₂,HfO₂/SiO₂, etc. Alternatively, the bottom mirror 400 may simply includeone or more metal layers, such as an Aluminum layer. It should berecognized that these are only illustrative, and that the bottom mirror400 may be made from any suitable material or material system thatprovides the desired reflectivity.

[0076] Next, and as shown in FIG. 13B, bottom electrodes 404 and bottomconducting pads 406 are provided. A dielectric or other protecting layer410 may be provided over the bottom electrodes 404 and bottom conductingpads 406 (see FIG. 13C). The dielectric or other protecting layer 410may then be patterned to expose the bottom conducting pads 406, as shownin FIG. 13C.

[0077] Next, and as shown in FIG. 13C, a first sacrificial layer 412 isprovided. The first sacrificial layer 412 is preferably polyimide, butmay be any suitable material. Next, and as shown in FIG. 13D, a topmirror 420 is provided. The top mirror 420 is preferably a DistributedBragg reflector that includes a semiconductor and/or dielectric mirrorstack. Like the bottom mirror 400, the Distributed Bragg reflector mayinclude, for example, a number of alternating layers of ZrO₂/SiO₂,HfO₂/SiO₂, etc. Alternatively, the top mirror 420 may simply include oneor more metal layers, such as one or more Aluminum layers. It should berecognized that these are only illustrative, and that the top mirror maybe made from any suitable material or material system that provides thedesired reflectivity. The top mirror 420 is then patterned, as shown inFIG. 13D. Then, a second sacrificial layer 422 is provided over thefirst sacrificial layer 412 and the patterned top mirror 420.

[0078] Next, and as shown in FIG. 13E, holes 424 are etched through thefirst sacrificial layer 412 and the second sacrificial layer 422 down tothe conductive pads 406. Next, a metal layer is deposited and patternedto form top electrode regions 430. The metal layer preferably extendsinto holes 424 to form an electrical connection with bottom conductingpads 406, as shown.

[0079] Next, and as shown in FIG. 13F, the portion of the secondsacrificial layer 422 above the top mirror 420 is removed. A supportlayer 440 is then provided over the top surface of the resultingstructure. The support layer 440 preferably bonds to the top mirror 420,and fills the holes 424. A buffer layer may be provided first to helpbond the layers, if desired. In a preferred embodiment, the supportlayer 440 is SiO₂, but this is not required.

[0080] Next, and as shown in FIG. 13G, the support layer 340 ispatterned to expose the top mirror 420. While a thin column member 442remains in FIG. 13G, this is not required. In addition, the top mirror420 is shown having a ridge in the central portion thereof. In someembodiments, this ridge may be eliminated, and the top mirror 420 may besubstantially planar. Also, the support layer 340 may be patterned todefine one or more elongated supporting legs, such as those shown anddescribed with respect to FIGS. 4-7 above.

[0081] Preferably the support layer 440 overlaps the outer perimeter ofthe top mirror 420, as shown. This overlap helps form a bond between thesupport layer 440 and the top mirror 420. Finally, and as shown in FIG.13H, a dry etch may be used to remove the first and second sacrificiallayers 412 and 422 to releases the top structure from the bottomstructure, as shown. The dry etch may be, for example, an oxygen plasmaetch. An anneal may be performed to help reduce the stress in thestructure, including in the SiO₂ support layer 440. The anneal may beperformed before or after the first and second sacrificial layers 412and 422 are removed, as desired.

[0082] The illustrative structure shown in FIGS. 13A-13H positions thetop electrodes 430 further from the bottom electrodes 404 than theembodiment shown in FIGS. 12A-12I. It has been found that under somecircumstances, the top electrodes 430 tend to snap down toward thebottom electrodes 404 when the distance between the top electrodes 430and the bottom electrodes 404 is reduced through electrostatic actuation(e.g. when the distance is reduced by about one-third). Therefore, toincrease the distance that the top mirror 420 can travel relative to thebottom mirror 400 without experiencing the snapping action, the topelectrode 430 has been purposefully moved further from the bottomelectrode 404. In addition, the top mirror 420 has been positioned belowthe top electrode 430, as shown.

[0083] FIGS. 14A-14K are schematic cross-sectional side views showingyet another illustrative method for making a tunable bandpass filter inaccordance with the present invention. Turning first to FIG. 14A, abottom mirror 450 is grown on a substrate 452. The substrate 452 may be,for example, Pyrex, sapphire or any other suitable material. The bottommirror 450 is preferably a Distributed Bragg reflector that includes asemiconductor and/or dielectric mirror stack. The Distributed Braggreflector may include, for example, a number of alternating layers ofZrO₂/SiO₂, HfO₂/SiO₂, etc. Alternatively, the bottom mirror 450 maysimply include one or more metal layers, such as an Aluminum layer . Itshould be recognized that these are only illustrative, and that thebottom mirror 450 may be made from any suitable material or materialsystem that provides the desired reflectivity.

[0084] Next, and as shown in FIG. 14B, bottom electrodes 454 and bottomconducting pads 456 are provided. The bottom electrodes 454 andconducting pads 456 are preferably deposit by lift-off, but any suitableprocess may be used. Next, and as shown in FIG. 14C, a dielectric orother protecting layer 460 may be provided over the bottom electrodes454 and bottom conducting pads 456. The dielectric or other protectinglayer 460 may then be patterned to expose the bottom conducting pads 456and the optical window area 463, as shown in FIG. 14C. Layer 460 may beany type of dielectric or other protecting layer including, for example,Alumina passivation.

[0085] Next, and as shown in FIG. 14D, a first sacrificial layer 472 isprovided and patterned in the optical window area 463. The firstsacrificial layer 472 is preferably about 4000A of metal, but may be anysuitable material. Next, and as further shown in FIG. 14D, a top mirror474 is provided. The top mirror 474 is preferably a Distributed Braggreflector that includes a semiconductor and/or dielectric mirror stack.Like the bottom mirror 450, the Distributed Bragg reflector may include,for example, a number of alternating layers of ZrO₂/SiO₂, HfO₂/SiO₂,etc. Alternatively, the top mirror 474 may simply include one or moremetal layers, such as one or more Aluminum layers. It should berecognized that these are only illustrative, and that the top mirror 474may be made from any suitable material or material system that providesthe desired reflectivity. The top mirror 474 is then patterned, as shownin FIG. 14D.

[0086] Next, and as shown in FIG. 14E, a second sacrificial layer 478 isprovided over the patterned top mirror 474. The second sacrificial layer478 is preferably about 8000A of polimide, but may be any suitablematerial. Next, and as shown in FIG. 14F, one or more holes 480 a and480 b are etched through the second sacrificial layer 478 down to theconductive pads 456 and the top mirror 474, respectively. The holes 480a and 480 b preferably do not extend all the way to the lateral edges ofthe conductive pads 456 and the top mirror 474, but this is notrequired.

[0087] Next, and as shown in FIG. 14G, a metal layer is deposited andpatterned to form top electrode regions 482. The metal layer 482preferably extends into hole 480 a to form an electrical connection withbottom conducting pads 456, as shown. The metal layer 482 preferably isremoved from above the top mirror 474.

[0088] Next, and as shown in FIG. 14H, a support layer 490 is providedover the top surface of the resulting structure. The support layer 490preferably bonds to the top mirror 474, and fills the hole 480 b. Abuffer layer may be provided first to help bond the layers, if desired.In a preferred embodiment, the support layer 490 is nominally about 3 μmof SiO₂, but other thicknesses and materials may be used.

[0089] Next, and as shown in FIG. 14I, the support layer 490 ispatterned to expose the top mirror 474. Preferably the support layer 490overlaps the outer perimeter of the top mirror 474, as shown. Thisoverlap helps form a bond between the support layer 490 and the topmirror 474. Also, the support layer 490 may be patterned to define oneor more elongated supporting legs, such as those shown and describedwith respect to FIGS. 4-7 above.

[0090] Next, and as shown in FIG. 14J, the first sacrificial layer 472is removed. In a preferred embodiment, the first sacrificial layer 472is removed with a wet etch to release the top mirror 474 from the bottommirror 450. It is contemplated that the first sacrificial layer 472 maybe made from a material that can be selectively etched relative to theremaining structure.

[0091] Next, and as shown in FIG. 14K, the second sacrificial layer 478is removed to releases the top structure from the bottom structure, asshown. In a preferred embodiment, this may be performed using a dry etchsuch as an oxygen plasma etch. An anneal may be performed to help reducethe stress in the structure, including in the SiO₂ support layer 490.The anneal may be performed before or after the first and secondsacrificial layers 472 and 478 are removed, as desired.

[0092] The illustrative structure shown in FIGS. 14A-14K positions thetop electrodes 482 further from the bottom electrodes 454 than theembodiment shown in FIGS. 12A-12I. It has been found that under somecircumstances, the top electrodes 482 tend to snap down toward thebottom electrodes 454 when the distance between the top electrodes 482and the bottom electrodes 454 is reduced through electrostatic actuation(e.g. when the distance is reduced by about one-third). Therefore, toincrease the distance that the top mirror 474 can travel relative to thebottom mirror 450 without experiencing the snapping action, the topelectrodes 482 have been purposefully moved further from the bottomelectrode 454. In addition, the top mirror 474 has been positioned belowthe top electrodes 482, as shown.

[0093] FIGS. 15A-15C are perspective views of an illustrative assemblyof a tunable bandpass filter in accordance with the present invention.FIG. 15A shows various components including a tunable bandpass filter550, a lead frame 552, a detector 554, readout electronics 556 and apackage 558. The tunable bandpass filter 550 is preferably similar tothe tunable bandpass filter 12 shown and described with reference toFIG. 1. More specifically, and in the illustrative embodiment, thetunable bandpass filter 550 may include a Micro Electro OpticalMechanical System (MEOMS) etalon fabricated on a front side of asubstrate. In FIG. 15A, the back side of the substrate is shown facingup, with peripheral bond pads for the tunable bandpass filter elementspositioned along two sides of the front side of the substrate.

[0094] The lead frame 552 is preferably fabricated so that the leads 560are in registration with the peripheral bond pads of the tunablebandpass filter 550. FIG. 15B shows the bond pads of the tunablebandpass filter 550 bonded to the individual leads 560 of the lead frame552. Once the bond pads on the tunable bandpass filter 550 are bonded tothe corresponding leads 560 on the lead frame 552, the outer frame 562of the lead frame 552 may be removed, as best shown in FIG. 15C. Theportion of the leads 560 that extend out past the perimeter of thetunable bandpass filter 550 provide a wire bond pad for wire bonding thetunable bandpass filter 550 to the package 558, as further describedbelow.

[0095] The detector 554 may be similar to the detector 14 of FIG. 1.That is, the detector 554 may be formed on a substrate, and positionedadjacent the tunable bandpass filter 550 to receive one or morewavelengths that are passed through the tunable bandpass filter 550.Readout electronics 556 may also be provided. The readout electronics556 are preferably fabricated on a separate substrate using conventionalintegrated circuit processing techniques. Metal pads (not explicitlyshown) may be provided on the readout electronics substrate to providean electrical connection to the detector 554, as further described abovewith respect to FIG. 1. Bump bonds, for example, may be used toelectrically connect one or more electrodes of the detector 554 tocorresponding metal pads on the readout electronics 556. Theillustrative readout electronics 556 also have peripheral bond padsalong two sides of the readout electronics substrate, as shown.

[0096] The illustrative package 558 has an internal cavity 566 forreceiving the readout electronics 556, detector 554, lead frame 552 andtunable bandpass filter 550. FIG. 15B shows the detector 454 and readoutelectronics 556 secured within the internal cavity 566 of the package558. FIG. 15B also shows the tunable bandpass filter 550 and the leadframe 552 before they are inserted into the internal cavity 566 of thepackage 558. In the illustrative embodiment, the bond pads oil thereadout electronics 556 extend along two opposing sides of the package558, and the bond pads for the lead frame extend along the other twoopposing sides of the package 558. Wire bond pads may be provided alongan upper ledge 568 of the package 558. FIG. 15C shows the tunablebandpass filter 550 and the lead frame 552 after they have been insertedinto the internal cavity 566 of the package 558. Bond wires may beprovided between the bond pads on the upper ledge 568 of the package 558to the bond pads of the lead frame and the bond pads of the readoutelectronics. A lid (not shown) may also be provided to seal the innercavity of the package. In some embodiments, the lid may provide a vacuumseal.

[0097]FIG. 16 is a perspective view of another illustrative assembly ofa tunable bandpass filter in accordance with the present invention. Theembodiment shown in FIG. 16 is similar to the shown in FIGS. 15A-15C.However, the package 570 of FIG. 16 includes an inner ledge 572 and anouter ledge 574 of bond pads. The inner ledge 572 is preferablypositioned lower than the outer ledge. Like above, the detector 554 andreadout electronics 556 are first secured in the internal cavity of thepackage 570. Before the tunable bandpass filter 550 is inserted,however, wire bonds or the like (not shown) are provided to electricallyconnect the bond pads of the readout electronics to the bond pads on theinner ledge 572 of the package 570.

[0098] The tunable bandpass filter 550 is secured to an inner packageframe 580, rather than just a lead frame. The illustrative inner packageframe 580 has metal pads that bond to bond pads on the substrate of thetunable bandpass filter 550. The inner package frame 580 is preferablysized to mate within an upper opening in the top surface of the package570. Bump bonds may then be used to bond peripheral bond pads on theinner package frame 580 to the bond pads on the outer ledge 574 of thepackage 570. It is also recognized that the inner package frame 580could have the same lateral dimensions as the package 570 withinterconnections along the edge of the package 570. The verticaldimensions of the package 570 are designed to put the top substrate andbottom detector in close proximity, on the order of a few thousandths ofan inch. Again, a lid (not shown) may be provided to seal the innercavity of the package, as desired.

[0099] It should be understood that this disclosure is, in manyrespects, only illustrative. Changes may be made in details,particularly in matters of shape, size, and arrangement of steps withoutexceeding the scope of the invention. The invention's scope is, ofcourse, defined in the language in which the appended claims areexpressed.

What is claimed is:
 1. A spectrally tunable detector, comprising: atunable bandpass filter having a first at least partially reflectiveplate and a second at least partially reflective plate separated by aseparation gap, the tunable bandpass filter is selectively tuned to abandpass wavelength by moving the first plate and/or the second platerelative to one another to change the separation gap; and a detectorpositioned adjacent the tunable bandpass filter to receive one or morewavelengths that are passed by the tunable bandpass filter and toprovide an output signal in response thereto.
 2. A spectrally tunabledetector according to claim 1 wherein the tunable bandpass filter andthe detector are fixed relative to one another.
 3. A spectrally tunabledetector according to claim 1 wherein the tunable bandpass filter isprovided on a first substrate and the detector is provided on a secondsubstrate, the first substrate and the second substrate beingsubstantially transparent to the one or more wavelengths that are passedby the tunable bandpass filter.
 4. A spectrally tunable detectoraccording to claim 3 wherein first substrate is fixed relative to thesecond substrate.
 5. A spectrally tunable detector according to claim 3wherein an incoming light beam enters the tunable bandpass filter andsubsequently passes through the first substrate.
 6. A spectrally tunabledetector according to claim 5 wherein the incoming light beamsubsequently enters the detector through the second substrate.
 7. Aspectrally tunable detector according to claim 6 wherein the first plateand the second plate of the tunable bandpass filter are positioned on asurface of the first substrate that is opposite to the surface that isadjacent the second substrate.
 8. A spectrally tunable detectoraccording to claim 7 further comprising a read out circuit provided on athird substrate.
 9. A spectrally tunable detector according to claim 8wherein the detector is electrically connected to the read out circuit.10. A spectrally tunable detector according to claim 8 wherein the thirdsubstrate is mounted to a package.
 11. A spectrally tunable detectoraccording to claim 3 wherein a lens is positioned adjacent the firstsubstrate.
 12. A spectrally tunable detector, comprising: a tunablebandpass filter for selectively passing a band of wavelengths from apredetermined spectral range of wavelengths, the tunable bandpass filterhaving an etalon with a top plate and a bottom plate that are separatedby a separation gap, both the top plate and the bottom plate having areflective portion that is at least partially reflective, the top plateand/or bottom plate adapted to move relative to the other plate to varythe separation gap across a predetermined range of separation gaps, theseparation gap at least partially determining the band of wavelengthsthat are passed by the tunable bandpass filter and the predeterminedrange of separation gaps at least partially determining thepredetermined spectral range of wavelengths; and a detector positionedadjacent the tunable bandpass filter, the detector being sensitive tothe predetermined spectral range of wavelengths.
 13. A spectrallytunable detector according to claim 12 wherein the etalon is a MicroElectro Optical Mechanical System (MEOMS) etalon.
 14. A spectrallytunable detector according to claim 13 wherein the bottom plate ispositioned atop a substrate.
 15. A spectrally tunable detector accordingto claim 14 wherein the top plate is positioned above the substrate, andmechanically connected to the substrate by one or more support legs. 16.A spectrally tunable detector according to claim 15 further includingone or more top electrodes coupled to the top plate.
 17. A spectrallytunable detector according to claim 16 further including one or morebottom electrodes coupled to the substrate.
 18. A spectrally tunabledetector according to claim 17 further comprising a control circuit forapplying a voltage between one or more of the top electrodes and one ormore of the bottom electrodes to pull at least part of the top platecloser to at least part of the bottom plate via an electrostatic forceto thereby reduce the separation gap between the reflective portion ofthe top plate and the reflective portion of the bottom plate.
 19. Aspectrally tunable detector according to claim 18 wherein the substrateis Pyrex.
 20. A spectrally tunable detector according to claim 12wherein the detector is an AlGaN diode.
 21. A spectrally tunabledetector according to claim 12 further comprising a lens for directingan incoming light beam to the tunable bandpass filter.
 22. A spectrallytunable detector according to claim 12 wherein the bandpass filter isadapted to allow only a single band of wavelengths from thepredetermined spectral range of wavelengths for each separation gap inthe predetermined range of separation gaps.
 23. A tunable bandpassfilter comprising: a substrate; a lower at least partially reflectivemirror secured to the substrate; one or more lower electrodes secured tothe substrate; an upper at least partially reflective mirror suspendedabove the lower mirror by a support member; and one or more upperelectrodes suspended above the one or more lower electrodes, the one ormore upper electrodes secured to the support member; whereby when avoltage is applied between the one or more lower electrodes and the oneor more upper electrodes, an electrostatic force causes at least part ofthe support member to move closer to the substrate which causes theupper mirror to move closer to the lower mirror.
 24. A tunable bandpassfilter according to claim 23 wherein the support member is secured tothe substrate through one or more posts that extend upward from thesubstrate.
 25. A tunable bandpass filter according to claim 24 whereinthe electrostatic force causes the support member to deform between oneor more of the posts and the upper mirror.
 26. A tunable bandpass filteraccording to claim 25 wherein the one or more upper electrodes areelectrically connected through one or more of the posts to a conductiveelement that is secured to the substrate.
 27. A tunable bandpass filteraccording to claim 25 wherein the voltage that is applied between afirst lower electrode and a first upper electrode is different from thevoltage that is applied between a second lower electrode and a secondupper electrode.
 28. A tunable bandpass filter according to claim 25wherein the upper at least partially reflective mirror is positionedcloser to the substrate than the one or more upper electrodes.
 29. Amethod for making a tunable bandpass filter, comprising: providing afirst substrate; providing a support layer adjacent the first substrate;providing an upper mirror adjacent the support layer; patterning theupper mirror; providing an upper electrode layer adjacent the supportlayer; patterning the upper electrode layer to provide one or more upperelectrodes; providing a second substrate; providing a lower mirroradjacent the second substrate; providing a lower electrode layeradjacent the second substrate; patterning the lower electrode layer toprovide one or more lower electrodes that are in substantialregistration with the one or more upper electrodes; providing one ormore posts that extend in an upward direction relative to the secondsubstrate; providing a sacrificial layer over the upper mirror and theone or more upper electrodes, and/or over the lower mirror and the oneor more lower electrodes; positioning the first substrate and the secondsubstrate together so that the upper mirror and the one or more upperelectrodes are facing and are in substantial registration with the lowermirror and the one or more lower electrodes, respectively, with thesacrificial layer situated therebetween; applying heat and pressure, andthen cooling; removing the first substrate; patterning the support layerto expose at least part of the upper mirror while maintaining amechanical connection between the upper mirror and the support layer;and removing the sacrificial layer.
 30. A method according to claim 29further comprising securing the support layer to one or more of theposts.
 31. A method according to claim 29 wherein the sacrificial layerproviding step includes: providing a first sacrificial layer of a firsttype over the lower mirror and the one or more lower electrodes;providing a second sacrificial layer of a second type over the firstsacrificial layer; and providing a third sacrificial layer of the secondtype over the upper mirror and the one or more upper electrodes.
 32. Amethod for making a tunable bandpass filter, comprising: providing asubstrate; providing a lower mirror above the substrate; providing alower electrode layer above substrate; patterning the lower electrodelayer to provide one or more lower electrodes and one or more upperelectrode pads; providing a sacrificial layer adjacent the one or morelower electrodes, the one or more upper electrode pads, and the lowermirror; providing holes through the sacrificial layer, selected holesbeing in registration with the one or more upper electrode pads;providing a conductive layer above the sacrificial layer; patterning theconductive layer to provide one or more upper electrodes that are inregistration with the one or more lower electrodes, and to provide aconductive path from the one or more upper electrodes to one or more ofthe holes; providing an upper mirror; providing a support layer over theupper mirror; patterning the support layer and any intervening layersbetween the support layer and the upper mirror to expose at least partof the upper mirror while maintaining a mechanical connection betweenthe upper mirror and the support layer; and removing the sacrificiallayer.
 33. A method according to claim 32 wherein the support layerextends into the one or more etched holes.
 34. A method according toclaim 32 wherein the conductive layer extends into the one or moreetched holes and makes electrical connection to the one or more upperelectrode pads.
 34. A method for making a tunable bandpass filter,comprising: providing a substrate; providing a lower mirror above thesubstrate; providing a lower electrode layer above substrate; patterningthe lower electrode layer to provide one or more lower electrodes andone or more upper electrode pads; providing a first sacrificial layeradjacent the lower mirror; providing an upper mirror adjacent the firstsacrificial layer; providing a second sacrificial layer above the uppermirror; providing holes through the second sacrificial layer, selectedholes being in registration with the one or more upper electrode padsand selected holes being in registration with the upper mirror;providing a conductive layer above the sacrificial layer; patterning theconductive layer to provide one or more upper electrodes that are inregistration with the one or more lower electrodes, and to provide aconductive path from the one or more upper electrodes to one or more ofthe holes and eventually to one or more upper electrode pads; providinga support layer adjacent the second sacrificial layer; patterning thesupport layer and any intervening layers between the support layer andthe upper mirror above at least part of the upper mirror whilemaintaining a mechanical connection between the upper mirror and thesupport layer; and removing the first and second sacrificial layers. 35.A method according to claim 34 wherein the first sacrificial layer isAlumina passivation.
 36. A method according to claim 34 wherein thesecond sacrificial layer is polyimide.
 37. A method according to claim34 wherein the first sacrificial layer is removed using a wet etch. 38.A method according to claim 34 wherein the second sacrificial layer isremoved using a dry etch.
 39. An electrostatically actuated structure,comprising: a substrate; one or more lower electrodes secured relativeto the substrate; one or more upper electrodes suspended above the oneor more lower electrodes; and the one or more upper electrodespositioned on a support layer, wherein the support layer has two or moreelongated legs that extend in at least two lateral directions away fromthe one or more upper electrodes, each leg is secured to a supportingpost that extends upward from the substrate.
 40. An electrostaticallyactuated structure according to claim 39 wherein the support layer hastwo legs, each leg extending on an opposite direction from the one ormore upper electrodes.
 41. An electrostatically actuated structureaccording to claim 40 wherein each of the two legs extends substantiallythe same distance from the one or more upper electrodes.
 42. Anelectrostatically actuated structure according to claim 39 wherein thesupport layer is “H” shaped having a first electrode leg portion and asecond electrode leg portion spaced from one another and connected by abridge portion, the first electrode leg portion having a first elongatedsupport leg extending outward in a first direction to a first supportingpost and a second elongated support leg extending outward in theopposite direction to a second supporting post, the second electrode legportion having a first elongated support leg extending outward in thefirst direction to a third supporting post and a second elongatedsupport leg extending outward in the opposite direction to a fourthsupporting post, the electrostatically actuated structure further havinganother support leg extending from the bridge portion in the spacebetween the first electrode leg portion and the second electrode legportion.
 43. An electrostatically actuated structure according to claim42 wherein the support leg extending from the bridge portion isconnected to a support structure that supports a mirror that issuspended above the substrate.
 44. An electrostatically actuatedstructure according to claim 39 wherein the support layer has a firstelectrode leg portion and a second electrode leg portion spaced from oneanother and connected by a bridge portion, the first electrode legportion and the second electrode leg portion being laterally offsetrelative to one other but overlapping at least at the bridge portion,the first electrode leg portion having a first elongated support legextending outward in a first direction to a first supporting post and asecond elongated support leg extending outward in the opposite directionto a second supporting post, the second electrode leg portion having afirst elongated support leg extending outward in the first direction toa third supporting post and a second elongated support leg extendingoutward in the opposite direction to a fourth supporting post, theelectrostatically actuated structure further having another support legextending from the bridge portion in the space between the firstelectrode leg portion and the second electrode leg portion.
 45. Anelectrostatically actuated structure according to claim 44 wherein thefirst electrode leg portion includes a first electrode and a secondelectrode, wherein the first electrode is positioned adjacent the bridgeportion and the second electrode §is positioned adjacent to butsubstantially electrically insulated from the first electrode.
 46. Anelectrostatically actuated structure according to claim 45 wherein thefirst electrode can be separately energized from the second electrode.47. An electrostatically actuated structure according to claim 45wherein the second electrode leg portion includes a first electrode anda second electrode, wherein the first electrode is positioned adjacentthe bridge portion and the second electrode is positioned adjacent tobut substantially electrically insulated from the first electrode.